Grafted copolymers highly absorbent to aqueous electrolyte solutions

ABSTRACT

The present invention provides graft copolymers that are highly absorbent to aqueous electrolyte solutions. The graft copolymer is formed by the graft polymerizing an effective amount of each of the following components together to provide a highly absorbent copolymer: 
     (a) graft polymerizing onto a first polymer selected from the group consisting of polysaccharide, polypropylene, polyethylene and other polyolefins, and at least one comonomer selected from the group consisting of acrylamide, methacrylamide, acrylonitrile, acrylic acid, methacrylic acid, alkali salts of acrylic acid, alkali salts of methacrylic acid, 3-methacrylamidopropyldimethylamine, 2-acrylamido-2-methylpropane sulfonic acid, alkali salts of 2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyloxyethane sulfonic acid, alkali salts of 2-methacryloyloxyethane sulfonic acid, and any combination of two or more thereof; and 
     (b) graft polymerizing therewith an ampholytic ion pair monomer comprising 
     (i) an ammonium cation 3-methacrylamidopropyldimethylammonium and 
     (ii) a sulfonate anion selected from the group consisting of 2-acrylamido-2-methylpropane sulfonate, 2-methacryloyloxyethane sulfonate, vinyl sulfonate, styrene sulfonate and any combination of thereof.

This application is a divisional application of prior application Ser.No. 07/919,073, filed Jul. 23, 1992, now U.S. Pat. No. 5,219,970, whichis a continuation under 37 C.F.R. 1.62, of application Ser. No.07/653,581, filed Feb. 11, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to graft copolymers made with3-methacrylamidopropyldimethylammonium (MPDMA)/sulfonate ion pairs whichare useful for absorbing aqueous electrolyte solutions. A further aspectof the invention relates to a method of using graft copolymers made with3-methacrylamidopropyldimethylammonium/sulfonate ion pairs for absorbingaqueous electrolyte solutions.

2. Description of the Prior Art

Polymers for absorbing aqueous electrolyte solutions are used innumerous commercial and industrial applications. For example, polymersare used to improve the water absorbency of paper towels and disposablediapers.

Though known water absorbing polymers are highly absorbent to deionizedwater, they are dramatically less absorbent to aqueous electrolytesolutions such as salt water, brine, and urine. For example, hydrolyzedcross-linked polyacrylamide absorbs 1,024 grams of deionized water pergram of polymer, but only 25 grams of synthetic urine per gram ofpolymers. Cross-linked polyacrylate absorbs 423 grams of deionized waterper gram of polymer, but only 10 grams of synthetic urine gram ofpolymers. Hydrolyzed cross-linked polyacrylonitrile absorbs 352 grams ofdeionized water per gram of polymer, but only 25 grams of syntheticurine per gram of polymer. Analogous starch grafted copolymers generallyhave very poor absorbency to synthetic urine.

It would be a valuable contribution to the art to develop graftcopolymers with high absorbency to aqueous electrolyte solutions. Italso would be a valuable contribution to the art to develop inexpensivegraft copolymers with high absorbency to aqueous electrolyte solutions.Furthermore, it would be a valuable contribution to the art to developbiodegradeable graft copolymers which were high absorbency to aqueouselectrolyte solutions. The market for these types of copolymers is largeand the uses are numerous. Therefore, seemingly small improvements inthe absorbency translate into large savings in the quantity of copolymerrequired to absorb these liquids and large savings to the consumer.

Thus, it is a object of the present invention to provide graftMPDMA/sulfonate copolymers which are highly absorbent to aqueouselectrolyte solutions.

Another object of the present invention is to provide highlybiodegradeable graft copolymers which are highly absorbent to aqueouselectrolyte solutions.

A further object of the present invention is to provide a method ofusing the graft copolymers of the present invention for absorbing anaqueous electrolyte solution comprising the step of contacting the graftcopolymers of the present invention with the aqueous electrolytesolution.

Further objects, features, and advantages of the present invention willbe readily apparent to those skilled in the art upon reading thedescription of the invention which follows.

SUMMARY OF THE INVENTION

The graft copolymers of the present invention are graft copolymersformed by:

(A) graft copolymerizing onto a first polymer selected from the groupconsisting of polysaccharide, polypropylene, polyethylene and otherpolyolefins, and at least one comonomer, selected from the groupconsisting of acrylamide, methacrylamide, acrylonitrile, acrylic acid,methacrylic acid, alkali salts of acrylic acid, alkali salts ofmethacrylic acid, 3-methacrylamidopropydimethylamine,2-acrylamido-2-methylpropane sulfonic acid, alkali salts of2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyloxyethanesulfonic acid, alkali salts of 2-methacryloyloxyethane sulfonic acid,N-vinyl-2-pyrrolidone and any combination of two or more thereof; and

(B) graft copolymerizing therewith an ampholytic ion pair monomer havingan ammonium cation and a sulfonate anion wherein

(i) the ammonium cation is 3-methacrylamidopropyldimethylammonium and

(ii) the sulfonate anion is selected from the group consisting of2-acrylamido-2-methylpropane sulfonate, 2-methacryloyloxyethanesulfonate, vinyl sulfonate, styrene sulfonate, and any combination oftwo or more thereof; wherein the first polymer, comonomers and ion pairmonomers are provided in amounts which are effective to produce a highlyabsorbent graft copolymer.

A further aspect of the invention relates to a method of absorbing anaqueous electrolyte solution comprising

(A) contacting a graft copolymers formed by

(i) graft copolymerizing onto a first polymer selected from the groupconsisting of polysaccharide, polypropylene, polyethylene and otherpolyolefins, and at least one comonomer selected from the groupconsisting of acrylamide, methacrylamide, acrylonitrile, acrylic acid,methacrylic acid, alkali salts of acrylic acid, alkali salts ofmethacrylic acid, 3-methacrylamidopropyldimethylamine,2-acrylamido-2-methylpropane sulfonic acid, alkali salts of2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyloxyethanesulfonic acid, alkali salts of 2-methacryloyloxyethane sulfonic acid,N-vinyl-2-pyrrolidone and any combination of two or more thereof; and

(ii) graft copolymerizing therewith an ampholytic ion pair monomerhaving a ammonium cation and a sulfonate anion wherein

(a) the ammonium cation is 3-methacrylamidopropyldimethylammonium; and

(b) the sulfonic anion is selected from the group consisting of2-acrylamido-2-methylpropane sulfonate, 2-methacryloyloxyethanesulfonate, vinyl sulfonate, styrene sulfonate and any combination of twoor more thereof; wherein the first polymer, comonomers and ion pairmonomers are provided in amounts which are effective to produce a highlyabsorbent graft copolymer; with an aqueous electrolyte solution.

DESCRIPTION OF THE INVENTION

The present invention provides graft copolymers that are highlyabsorbent to aqueous electrolyte solutions. The graft copolymers of thepresent invention utilize an ampholytic ion pair composed of a3-methacrylamidopropyldimethylammonium cation and a sulfonate anion.

Graft copolymers as used herein are polymers of one or more species ofmonomers connected to a main chain as a side chain, exclusive of branchpoint on the main chain. Side chains of a graft copolymer aredistinguished from the main polymer chain by the monomer constitution ofthe side chain i.e., the side chains comprise units derived from atleast one species of monomer different from those that supply the unitsof the main polymer chain. The main polymer chain as utilized in thepresent invention are homopolymeric and copolymeric polymer such aspolysaccharide, polypropylene, polyethylene and other polyolefins. Theside chains are formed of olefinic comonomers and ampholytic ion pairs.

The term "graft copolymerization" is used herein, unless otherwiseindicated, to a main a copolymer which results from the formation of anactive site or sites at one or more points on the main chain of apolymer molecule other than its end and exposure to at least one othermonomer. The graft copolymers of the present invention comprise graftcopolymers formed by graft copolymerization of an effective amount ofeach of the following components onto a first polymer (main polymerchain) to produce a highly absorbent copolymer:

(A) at least one comonomer selected from the group consisting ofacrylamide, methacrylamide, acrylonitrile, acrylic acid, methacrylicacid, alkali salts of acrylic acid, alkali salts of methacrylic acid,3-methacrylamidopropyldimethylamine, 2-acrylamido-2-methylpropanesulfonic acid, alkali salts of 2-acrylamido-2-methylpropane sulfonicacid, 2-methacryloyloxyethane sulfonic acid, alkali salts of2-methacryloyloxyethane sulfonic acid, N-vinyl-2-pyrrolidone andcombination of two or more thereof; to form a first graft copolymer and

(B) an ampholytic ion pair monomer comprising

(i) the ammonium cation 3-methacrylamidopropyldmethylammonium (alsoreferred to as MPDMA) and

(ii) a sulfonate anion selected from the group consisting of2-acrylamido-2-methylpropane sulfonate (also referred to as AMPS® atrademark of Lubrizol for 2-acrylamido-2-methylpropane sulfonic acid),2-methacryloyloxyethane sulfonate (also referred to as MES), vinylsulfonate and styrene sulfonate and any combination thereof.

Polymer or copolymer which may be used as main chains in the practice ofthe present invention include polysaccharides, polypropylene,polyethylene and other polyolefins. Polysaccharides suitable for thepractice of the present invention include starches, cellulose andglycogens. Common source of cellulose include but are not limited tocotton, linen, rayon, wood pulp and cellulose xanthine. Currently,cotton gauze is preferred. Suitable starches included swollen amyloseand amylopectin starches. For the practice of the present invention,these starches should be swollen by heating the starch in water tosubstantially dissolve the starch granules. Preferably starches used inthe present invention will have less than 30 weight percent amylosebased on the weight of the dry starch before graft copolymerization. Thepreferred starch for use in grafting is soluble starch flour with in therange of from about 0 to about 20 weight percent amylose content.Polypropylene polymer suitable for use as main polymer chain includepolypropylene homopolymers, polypropylene copolymers and polypropyleneblock-copolymers. Polyethylene polymers suitable for use as a mainpolymer chain include polyethylene homopolymer, polyethylene copolymersand polyethylene block-copolymers. Preferably the synthetic polymerslisted above will be utilized in the form of filaments or thin sheets sothat a high surface area to mass will be provided for grafting thecomonomers and ampholytic ion pair onto. Filaments utilized for graftingwill preferably have a denier ranging from about 1 to about 20 denierand most preferably from in the range of about 1 to 8 denier.

The term "monomer" is used generically, unless otherwise indicated, tomean monomers, comonomers, termonomers, tetramonomers, etc. The term"comonomer" is used generically, unless otherwise indicated, to meanmonomers, comonomers, termonomers, tetramonomers, etc. for polymerswherein there are at least two different monomers.

The term "polymers" is used unless otherwise indicated, to meanhomopolymers, copolymers, terpolymers, tetrapolymers, etc., and graftedcopolymers thereof. The term "copolymer" is used generically, unlessotherwise indicated, to mean copolymers, terpolymers, tetrapolymers,etc., thus includes polymer prepared using two or more differentmonomers.

The olefinic comonomers can include but are not limited to the groupconsisting of acrylamide, methacrylamide, acrylonitrile, acrylic acid,methacrylic acid, alkali salts of acrylic acid, alkali salts ofmethacrylic acid, 3-methacrylamidopropyldimethylamine,2-acrylamido-2-methylpropane sulfonic acid, alkali salts of2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyloxyethanesulfonic acid, alkali salts of 2-methacryloyloxyethane sulfonic acid andN-vinyl-2-pyrrolidone.

As used in this application, the term "alkali salts" is usedgenerically, unless otherwise indicated to mean alkali salts includingbut not limited to lithium, sodium, potassium, and ammonium cations.

The ampholytic ion pair monomer used in the present invention may beprepared by titrating an aqueous solution of a sulfonic acid monomer topH 7 with 3-methacrylamidopropyldimethylamine at a temperature of about0°-15° C. The resulting aqueous solution containing the ampholytic ionpair may be purified by contacting the aqueous solution one or moretimes with small quantities of activated charcoal. The concentration ofthe ampholytic ion pair in the aqueous solution may be determined byevaporatively drying a known amount of the aqueous solution andweighting the residue.

Alternatively, the ampholytic ion pair monomer for use in thepreparation of the present invention may be prepared by methods whichare well known to those skilled in the art. For example, one of theampholytic ion pair monomers can be prepared by reacting3-methacrylamidopropyldimethylamine with commercially available2-acrylamido-2-methylpropane sulfonic acid or 2-methacryloyloxyethanesulfonic in anhydrous tetrahydrofuran. See J. C. Salamone, C. C. Tsai,A. P. Olson, and A. C. Watterson, Adv. Chemical Series, Volume 187,pages 337-346.

The polymers of the present invention were generally prepared in a twostep process, though a single graft copolymerizing step or more than twografting and polymerizing steps may be advantageously employed. Thepurpose of the two step process is to provide a first grafted polymerwherein the grafted ion pair monomer. Some systems mays may be reactiveenough so that a two step process is not necessary to provide graftedcopolymers which are highly absorbent to aqueous electrolyte solutions.Alternatively, the multiple step process may be advantageously employedto control the proportions of monomers and relative lengths of the blockcopolymer chains by graft copolymerizing the various monomers in thedesired stoichiometric ratios at the appropriate step of the process.

In the preparation of polysaccharide graft MPDMA/sulfonate copolymers itis preferred that as a first step, at least one of the comonomers isgraft copolymerized onto a polysaccharide, to produce a firstpolysaccharide graft copolymer. Then in a second step, the ampholyticion pair is graft copolymerized onto the polysaccharide or theampholytic ion pair is polymerized onto the grafted comonomer sidechains. At the second or any subsequent graft copolymerizing step, theampholytic ion pair monomer may be copolymerized with at least one othercomonomer. At the second step or any subsequent graft copolymerizingstep, the ampholytic ion pair monomer may be copolymerized with at leastone comonomer which has a polymerizable olefinic functionality selectedfrom the group consisting of acrylamide (also referred to as AM),methacrylamide, acrylonitrile (also referred to as AN), acrylic acid(also referred to as AA), methacrylic acid, alkali salts of acrylic acid(also referred to as X-AA), alkali salts of methacrylic acid,3-methacrylamidopropyldimethylamine, 2-acrylamido-2-methylpropanesulfonic acid, alkali salts of 2-acrylamido-2-methylpropane sulfonicacid, 2-methacryloyloxyethane sulfonic acid, alkali salts of2-methacryloyloxyethane sulfonic acid, N-vinyl-2-pyrrolidone and anycombination of two or more thereof.

The polymerization of the ampholytic ion pair may be require a highertemperature then the polymerization of some of the other comonomers.Therefore, for the polymerization of the ampholytic ion pair it isdesirable to perform the polymerization at temperatures in the range offrom about 0° C. to about 90° C. and preferably in the range of fromabout 40° C. to about 70° C. Those skilled in the art will recognizethat the temperature at which the polymerization is carried out shouldbe varied to allow the various monomers and comonomer to reactcompletely within a reasonable period of time for the method ofpolymerization utilized.

Most graft copolymerization methods for olefinic monomers involve thecreation of reactive sites (for example free-radicals) on the mainpolymer chain. These reactive sites then serve to initiate thecopolymerization of the other monomers onto the main copolymer chain.Free-radicals reactive sites on the main chain generally are produced byhigh energy radiation or chemical initiation. A common chemical meansfor creating these free-radicals within polymerization polymers andpolypropylene polymers is with a chemical oxidation-reduction system.Examples of such oxidation-reduction systems include but are not limitedto oxidation-reduction systems selected from the group consisting ofceric ammonium nitrate/nitric acid, ceric ammonium sulfate/sulfuricacid, potassium permanganate/oxalic acid, hydrogen peroxide/ferrousalkali salts, hydrogen peroxide/ascorbic acid and amine/persulfate.Common irradiation means for producing free radicals on the main polymerchain is by utilizing a gamma radiation source (i.e. cobalt 60) or anelectron beam.

The copolymerization of the ampholytic ion pair monomer with theolefinic comonomer onto the grafted comonomer side chains can beachieved by any of the well known free-radical polymerization techniquesin solution, suspension, or emulsion environment. Well known azocompounds commonly employed to initiate free radical polymerizationreactions include 2,2'-azobis(N,N'-dimethylisobutyramidine)dihydrochloride, azobisisobutyronitrile, 4,4'-azobis(4-cyanovalericacid), 2,2'-azobis(2,4-dimethyl(4-methyoxyvalernitrile),2,4'-azobis(2,4-dimethylvaleronitrile),2,2'-azobis(2-amidopropane)dihydrochloride,2-t-butylazo-2-cyano-4-methoxy-4-methylpentane,2-t-butylazo-2-cyano-4-methylpentane, and 4-t-butylazo-4-cyanovalericacid. Well known inorganic peroxide compounds commonly employed toinitiate from radical polymerization reactions include hydrogenperoxide, alkali metal persulfates, alkali metal perborates, alkalimetal perphosphates, and alkali metal percarbonates. Well known organicperoxide compounds commonly employed to initiate free radicalpolymerization reactions include lauryl peroxide,2,5-dimethyl-2,5-bis(2-ethylhexanylperoxy)hexane, t-butylperoxypivilate,t-butylperoctoate, p-menthane hydroperoxide, and benzoylperoxide. Thecompound t-butylhyponitrite is a well known alkyl hyponitrite commonlyemployed to initiate free radical polymerization reactions. Furthermore,ultraviolet light is commonly employed to initiate free radicalpolymerization reactions with olefinic monomers. In addition, such othermethods of copolymerization as would have occurred to one skilled in theart may be employed, and the present invention is not limited to theparticular method of preparing the polymer set out herein. Theappropriate conditions under which polymerization reaction describedabove are well known in the art.

Optionally the inventive graft copolymers of the present invention canbe crosslinked with a suitable crosslinking agent including but notlimited to the group consisting of N,N-diallylmethacrylamide,diallylamine, N,N-bisacrylamidoacetic acid, N,N'-bisacrylamidoaceticacid methylester, N,N'-methylenebisacrylamide(methylene-bis-acrylamide), N,N-benzyldienebisacrylamide, allylacrylate,diisopropenylbenzene, diallylsuccinate, ethyleneglycol diacrylate,diallylacrylamide, divinylbenzene, and combinations of two or morethereof. The crosslinking agent should be admixed with the monomer orcomonomers when the side chain are being formed from the main polymerchain. The amount of crosslinking agent admixed with the monomers orcomonomers will be in the range of from about 0.01 to about 0.2 weightpercent of total weight of monomers and comonomers in the graftcopolymerization reaction.

The graft copolymers containing an olefinic comonomer with amide,nitrile, carboxylic acid, or sulfonic acid functionalities canoptionally be at least partially hydrolyzed and/or neutralized byheating with aqueous base such as aqueous sodium hydroxide or aqueouspotassium hydroxide. As used in this herein, the term "hydrolysis" isused generically, unless otherwise indicated, to include hydrolysis ofnitrile functionalities and hydrolysis of amide functionalities. Thesehydrolysis reactions are loosely referred to in the art as"saponification." Hydrolysis of these functionalities may occur underacidic or basic conditions. Under basic hydrolysis conditions, the termalso includes, unless otherwise indicated, neutralization of carboxylicacid and sulfonic acid functionalities. The degree of hydrolysis and/orneutralization can be controlled by stoichiometrically limiting theamount of base relative to the amount of amide, nitrile, carboxylicacid, and sulfonic acid functionalities.

The relative amount of the main polymer chain to the total weight of thecomonomer and ampholytic ion pair can be choosen to provide a graftcopolymer of variable absorbency. However, it is preferred that the mainpolymer chain constitutes in the range of from about 1 to about 50weight percent of the total weight of comonomers, ampholytic ion pairand main polymer chain present and most preferably it is preferred thatthe amount of main polymer chain be in the range from about 5 to about30 weight percent. The mole percent of comonomer and ampholytic ion pairwhich may be graft copolymerized onto the main polymer chain is given inTables I and II (these mole percents are based on the total moles of thecomonomers and ampholytic ion pair totaling a 100 percent).

                  TABLE I                                                         ______________________________________                                        Broad Comonomer Compositions for the Graft Copolymers                         MPDMA/sulfonate  AM        AN      X-AA                                       MOLE PERCENT                                                                  ______________________________________                                        broad  2-25          --        98-75 --                                       broad  2-20          98-80     --    --                                       broad  2-20          --        --    98-80                                    ______________________________________                                         MPDMA/sulfonate = 3methacrylamidopropyldimethylammonium cation/ a             sulfonate anion selected from the group consisting of                         2acrylamido-2-methylpropane sulfonate, 2methacryloyloxyethane sulfonate       and any combination thereof                                                   AM = Acrylamide                                                               AN = Acrylonitrile                                                            X-AA = Alkali Salt of Acrylic Acid                                       

                  TABLE II                                                        ______________________________________                                        Preferred Comonomer Compositions for the Graft Copolymers                     MPDMA/                                                                        AMPS ®   MPDMA/MES   AM      AN    X-AA                                   MOLE PERCENT                                                                  ______________________________________                                        preferred                                                                            5-25      --          --    75-95 --                                   preferred                                                                            --        5-20        --    80-95 --                                   preferred                                                                            5-20      --          95-80 --    --                                   preferred                                                                            --        10-20       90-80 --    --                                   preferred                                                                            3-15      --          --    --    97-85                                preferred                                                                            --        3-10        --    --    97-90                                ______________________________________                                         MPDMA/MES = 3methacrylamidopropyldimethylammonium                             cation/2methacryloyloxyethane sulfonate                                       MPDMA/AMPS ® = 3-methacrylamidopropyldimethylammonium                     cation/2acrylamido-2-methylpropane sulfonate                                  AM = Acrylamide                                                               AN = Acrylonitrile                                                            X-AA = Alkali Salt of Acrylic Acid (Acrylate)                            

The polysaccharide grafted polymers of the present invention should behighly biodegradable because the main chain of the graft copolymer ishighly biodegradable.

A further aspect of the invention relates to a method of absorbingaqueous electrolyte solutions comprising the step of contacting thepolymers of the present invention with the aqueous solution. Typicalaqueous electrolyte solutions include but are not limited to electrolytesolutions selected from the group consisting of tap water, salt water,brine, and urine. For the purpose of this invention, tap water isdefined to have an electrolyte concentration of less than 500 ppm ofdissolved electrolytes, urine is defined to have an electrolyteconcentration of from greater than 500 ppm to at most 10,000 ppm ofdissolved electrolytes, salt water is defined to have an electrolyteconcentration from greater than 10,000 ppm to at most 34,000 ppm andbrine is defined to have an electrolyte concentration of from greaterthan 34,000 ppm to the saturation point of the solution.

The following examples are intended to illustrate the advantages of thisinvention but are not intended to unduly limit this invention.

EXAMPLE I

The control data in Table III demonstrates that although knowncrosslinked polymers are highly absorbent to deionized water, they aredramatically less absorbent to aqueous electrolyte solutions such assalt water and urine. Polysaccharide grafted polymers, however,according to their inherent nature, are normally much less absorbent toaqueous liquids. The polysaccharide substrate, which comprises a largeportion of the material, is very poorly absorbent to aqueous liquids ofall kinds. This control data can be used to show that the polysaccharidegrafted MPDMA/sulfonate copolymers of the present invention caneffectively compete with these known crosslinked polymers and exceed theabsorbency of these known crosslinked polymers. Furthermore, these knowncross-linked polymers have questionable biodegradeability.

Known polymer compositions include crosslinked polyacrylamide, partiallysaponified crosslinked polyacrylamide, crosslinked polyacrylonitrile,partially saponified cross-linked acrylonitrile, cross-linkedpolyacrylic acid, neutralized crosslinked polyacrylic acid, cross-linkedpolyacrylate, and polymers thereof with sodium2-acrylamido-2-methylpropane sulfonate. The best of these known polymersabsorbs up to about 60 grams of urine per gram of polymer, and most ofthe known polymers absorb much less than 50 grams of urine per gram ofpolymer.

The crosslinked polymers of the control data were prepared by mixing themonomers in the proportions given in Table III in an aqueous solution ofdeionized water. The monomers were present in about 30-40 weight percentrelative to the amount of deionized water. The free radicalpolymerization was initiated with commercially available2,2'-azobis(N,N'-dimethylisobutyramidine) dihydrochloride. The reactionmixture was then degassed by bubbling nitrogen gas through the mixturefor 15 minutes. About 0.1 mole percent based on the total moles of themonomers of the azo free-radical initiator was employed. The reactiontemperature was maintained between 20°-35° C. for 24 hours. Thereactions produced transparent or cloudy hard gels of the crosslinkedpolymers. A large volume of deionized water was added to the polymerproduct and the polymers were allowed to swell for about 24 hours. Theswelled polymers were dried in a force convection oven at 74° F. Thedried polymers were then mechanically blended into a powder.

Some of the crosslinked polymers were hydrolyzed or neutralized with astrong base such as aqueous sodium hydroxide or aqueous potassiumhydroxide. The degree of hydrolysis or neutralization could becontrolled by stoichiometrically limiting the amount of base relative tothe amount of amide, nitrile, or carboxylic acid functionalities. Forthese examples, a stoichiometric excess of the amount of base was used.A suspension of 1 gram of the polymer in about 20 milliliters of 0.5molar aqueous sodium hydroxide was heated to 95° C. until a lightgolden-yellow color was obtained. The mixture was then transferred to adialysis bag with a molecular weight cut-off of 12,000-14,000 anddialyzed exhaustively against distilled water until the viscous polymergel had reached pH 7. This viscous polymer gel was then poured into aplastic dish and dried in a forced convection oven at 74° C. The driedpolymers were then mechanically blended to a powder.

The crosslinked polymers were then tested for deionized water absorptionand synthetic urine absorption. About 1 liter of deionized water orsynthetic urine was added to 0.1 to 0.5 gram of the dried polymer andallowed to stand for 24 hours. The polymer was then separated from theexcess unabsorbed liquid by screening through a 100 mesh per inchstainless steel sieve. The absorbency was determining by weighing theisolated polymer containing the absorbed liquid and subtracting theweight of the dry polymer. The absorbency was measured in units of gramsof liquid per grams of polymer. The synthetic urine was prepared bydissolving 0.64 gram CaCl₂, 1.14 gram MgSO₄.7H₂ O, 8.20 gram NaCl, and20.0 gram urea into 1000 gram deionized water. Several of the polymerswere tested two or three times, and the experimental error was withinplus or minus 2-5 percent. This small experimental error was largelycaused by gel blocking and minor diffusion problems that prevented theaqueous liquid from contacting with all the polymer.

                                      TABLE III                                   __________________________________________________________________________    Control Data For Known Cross-Linked Polymers                                  AMPS ®                                                                             AM AN AA X-AA LINK      DIW                                                                              SU                                        EXP #                                                                             MOLE PERCENT       mole ratio*                                                                         XOH g/g**                                        __________________________________________________________________________    126A                                                                              --   100                                                                              -- -- --   0.05  NO   17                                                                              15                                        126 --   100                                                                              -- -- --   0.05  YES 1024                                                                             25                                        406R                                                                              --   100                                                                              -- -- --   0.05  YES 364                                                                              40                                        125A                                                                              --   100                                                                              -- -- --   0.20  NO   13                                                                              12.5                                      125 --   100                                                                              -- -- --   0.20  YES 295                                                                              16                                         26 --   -- 100                                                                              -- --   0.05  YES 608                                                                              46                                        405 --   -- 100                                                                              -- --   0.10  NO   0 0                                         405 --   -- 100                                                                              -- --   0.10  YES 414                                                                              42                                        129 --   -- 100                                                                              -- --   0.20  YES 352                                                                              25                                        127A                                                                              --   -- -- 100                                                                              --   0.20  NO   21                                                                              11                                        127 --   -- -- 100                                                                              --   0.20  Neutr.                                                                            423                                                                              10                                        194 --   -- -- -- 100(K)                                                                             0.05  NO  669                                                                              57                                        204 --   -- -- -- 100(Na)                                                                            0.05  N0  505                                                                              41                                        211 --   13 -- --  87  0.05  NO  -- 65                                        267 3    13 -- --  84  0.05  NO  350                                                                              38                                        372 3    20 -- --  77  0.05  NO  417                                                                              47                                         20 6    13 -- --  81  0.05  NO  738                                                                              56                                         21 6    26 -- --  68  0.05  NO  533                                                                              47                                         22 6    -- -- --  94  0.05  NO  488                                                                              55                                         23 10   13 -- --  77  0.05  NO  570                                                                              59                                         25 20   13 -- --  67  0.05  NO  624                                                                              62                                         19 100  -- -- -- --   0.05  NO  Soluble                                      __________________________________________________________________________     AMPS ® = 2-acrylamido-2-methylpropane sulfonate (Note: AMPS ®  is     a trademark of Lubrizol for 2acrylamido-2-methylpropane sulfonic acid.)       AM = Acrylamide                                                               AN = Acrylonitrile                                                            AA = Acrylic Acid                                                             X-AA = Sodium Acrylate or Potassium Acrylate                                  LINK =Methylenebis-acrylamide CrossLinking Agent                              XOH = Basic Hydrolysis and/or Neutralization with aqueous NaOH or KOH         DIW = Deionized Water                                                         SU = Synthetic Urine                                                          *mole ratio = mole of the crosslinking agent per 100 mole of the              ampholytic ion pair monomer and the comonomer                                 **g/g = absorbency units of gram aqueous liquid per gram dried polymer   

EXAMPLE II

The control data in Table IV demonstrates that although commerciallyavailable water absorbing materials are highly absorbent to water, theyare also dramatically less absorbent to aqueous electrolyte solutionssuch as salt water and urine. The commercially available water absorbingmaterials tested include poly(co-acrylamide-co-acrylic acid) graftedonto starch, a commercial acrylamide polymer sold under the trademark"Water Grabber"® ("Water Grabber" is a trademark of F. P. Products,Inc.), "LUVS"® diaper absorbent ("LUVS" is a trademark of Procter &Gamble Co.), "Pampers"® diaper ("Pampers" is a trademark of Procter &Gamble Co.), and "Favor 960"® (Stockhausen, Inc.). The best of theseknown materials absorb up to about 56 grams of urine per gram ofabsorbing material, and most of the known polymers absorb much less than40 grams of urine per gram of absorbing material.

The commercially available materials were tested for absorbency toaqueous liquids according to the method employed in Example I.

                  TABLE IV                                                        ______________________________________                                        Control Data For Commercial Materials                                                                 D/W   SU                                              EXP # Commercial Material     g/g                                             ______________________________________                                        1     COMMERCIAL STARCH-g-POLY                                                                              345     37                                            (AM-AA)                                                                 2     WATER GRABBER ® (AM 440     34                                            COPOLYMER)                                                              3     LUVS ® DIAPER ABSORBENT                                                                           191     16                                      4     PAMPERS ® DIAPER ABSORBENT                                                                        171     12                                      5     FAVOR 960 ®         369     56                                      ______________________________________                                         g = graft                                                                     AM = Acrylamide                                                               AA = Acrylic Acid                                                             DIW = Deionized Water                                                         SU = Synthetic Urine                                                          *g/g = absorbency units of gram aqueous liquid per gram dried polymer    

EXAMPLE III

The homopolymers of the ampholytic ion pair monomers comprising3-methacrylamidopropyldimethylammonium 2-acrylamido-2-methylpropanesulfonate (MPDMA/AMPS) (AMPS® is a trade of Lubrizol Corporation for2-acrylamido-2-methylpropane sulfonic acid) or3-methacrylamidopropyldimethylammonium 2-methacryloyloxyethane sulfonate(MPDMA/MES) with 0.05 weight percent methylene-bis-acrylamidecrosslinking agent was tested for their absorbency to deionized waterand synthetic urine according to the method employed in Example I. Theabsorbency of homopolymers is very poor. See Table V. The absorbency todeionized water is about 10 grams water per gram of homopolymer, andonly 23 and 17 gram synthetic urine per gram of homopolymer,respectively.

                  TABLE V                                                         ______________________________________                                        Control Data For Ion Pair Homopolymer                                         MPDMA/      MPDMA/                                                            AMPS ®  MES       LINK           DIW  SU                                  EXP # MOLE PERCENT    mole ratio*                                                                             graft                                                                              g/g**                                    ______________________________________                                        319   100       --        0.05    --   10   23                                100   --        100       0.05    --   12   17                                ______________________________________                                         MPDMA/AMPS ® = 3-methacrylamidopropyldimethylammonium cation              2acrylamido-2-methylpropane sulfonate anion                                   MPDMA/MES = 3methacrylamidopropyldimethylammonium cation                      2methacryloyloxyethane sulfonate anion                                        LINK = Methylenebis-acrylamide CrossLinking Agent                             DIW = Deionized Water                                                         SU = Synthetic Urine                                                          *mole ratio = mole of the crosslinking agent per 100 mole of the              ampholytic ion pair monomer and the comonomer                                 **g/g = absorbency units of gram aqueous liquid per gram dried polymer   

EXAMPLE IV

The control data in Table VI demonstrates that although the knownampholytic ion pair 3-methacrylamidopropyltrimethylammonium2-acrylamido-2-methylpropane sulfonate (MPTMA/AMPS®) copolymerized withacrylamide is highly absorbent to deionized water, it is dramaticallyless absorbent to aqueous electrolyte solutions. The absorbency to urineis about the same as for the better of the known polymers and commercialmaterials. The MPTMA/AMPS®-acrylamide copolymer also has been graftedonto starch using ceric ion or cobalt-60 irradiation. These starchgrafted copolymers are poorly absorbent to deionized water, and onlyslightly more absorbent to synthetic urine. The better of these knownpolymers absorbs up to about 56 grams of urine per gram of polymer, butthe starch grafted polymers absorb less than 30 grams of urine per gramof polymer.

The MPTMA/AMPS®-acrylamide copolymers and starch grafted copolymersthereof were tested according to the method employed in Example I.

                  TABLE VI                                                        ______________________________________                                        Control Data For Known MPTMA/AMPS-Acrylamide                                  Copolymers                                                                    MPTMA/                                                                        AMPS ®  AM     Starch  LINK    DIW   SU                                   EXP # MOLE PERCENT     mole ratio*                                                                             g/g**                                        ______________________________________                                              10        90     --    --      soluble                                  87    10        90     --    0.20    428   56                                 **    8.56      27.30  64.86 --      9.83  16.21                              **    8.98      41.76  49.26 --      11.54 16.62                              **    15.01     64.96  20.03 --      14.11 29.45                              ______________________________________                                         MPTMA/AMPS ® = 3-methacrylamidopropyltrimethylammonium                    cation/2acrylamido-2-methylpropane sulfonate anion                            AM = Acrylamide                                                               LINK = Methylenebis-acrylamide CrossLinking Agent                             DIW = Deionized Water                                                         SU =Synthetic Urine                                                           *mole ratio = mole of the crosslinking agent per 100 mole of the              ampholytic ion pair monomer and the comonomer                                 **g/g = absorbency units of gram aqueous liquid per gram dried polymer        ***J. C. Salamone, E. L. Rodriguez, K. C. Lin, L. Quach, A. C. Watterson      and I. Ahmed, Polymer 26, 1234-38 (1985).                                

EXAMPLE V

The polysaccharide grafted MPDMA/sulfonate copolymers of the presentinvention in Tables VII and VIII were generally prepared according tothe following two step procedure.

About 10 grams of reagent grade soluble starch was added to 70milliliters of deionized water. While stirring under inert nitrogenatmosphere, the soluble starch slurry was heated to 95° C. for 1 hr.after which the heat was removed and the stirred soluble starch slurrywas allowed to cool to room temperature, about 22° C. A solution of 0.25gram ceric ammonium nitrate in 2 milliliters 1N nitric acid was added tothe cooled stirring soluble starch slurry. After about 1 minute, theolefinic comonomer (0.1884-0.2547 moles) was then added to the solublestarch slurry mixture. The particular comonomer and relative molepercent added for each of the tested polysaccharide graftedMPDMA/sulfonate copolymers is provided in Tables VII and VIII. Themixture was stirred under inert nitrogen atmosphere for two hours.

The mixture was then heated to 60° C., at which point a solution of 0.18g ceric ammonium nitrate in 1.5 milliliters 1N nitric acid was added tothe mixture. After about 1 minute, a 32 weight percent solution of theampholytic ion pair monomer dissolved in deionized water was added tothe warmed mixture. The particulate MPDMA/sulfonate monomer and relativemole percent added for each of the tested polysaccharide graftedMPDMA/sulfonate copolymers is provided in Tables VII and VIII. This newmixtures was stirred under nitrogen at 60° C. for another 4 hours.

The pH of the mixture was adjusted to between pH 4 and pH 5. The solidcrude polysaccharide grafted MPDMA/sulfonate copolymer was obtained byevaporating the aqueous solvent is a forced convection oven maintainedat 74° C. The crude grafted polymer was washed by boiling indimethylformamide to remove any non-grafted acrylonitrile homopolymer.It was then thoroughly washed with deionized water to remove any watersoluble polymer. The purified grafted material was finally washed withethanol and dried in a vacuum oven at 60° C. for 24 hours. The driedpolymers were then mechanically blended to a powder. The yield ofpolysaccharide grafted MPDMA/sulfonate copolymer was typically between60 and 90 percent based on the total weight of the soluble starch,comonomer, and ampholytic ion pair monomer.

Some of the inventive polysaccharide grafted MPDMA/sulfonate copolymerscontaining an olefinic comonomer with amide, nitrile, carboxylic acid,or sulfonic acid functionalities were hydrolyzed and/or neutralized withan aqueous base such as aqueous sodium hydroxide or aqueous potassiumhydroxide. The degree of hydrolysis or neutralization could becontrolled by stoichiometrically limiting the amount of base relative tothe amount of amide, nitrile, or carboxylic acid functionalities. Forthese examples, a stoichiometric excess of the amount of base was used.A suspension of 1 gram of the polymer in about 20 milliliters of 0.5molar aqueous sodium hydroxide was heated to 95° C. until a lightgolden-yellow color was obtained. The mixture was then transferred to adialysis bag with a molecular weight cut-off of 12,000-14,000 anddialyzed exhaustively against distilled water until the viscous polymergel had reached pH 7. This viscous polymer gel was then poured into aplastic dish and dried in a forced convection oven at 74° C. The driedpolymers were then mechanically blended to a powder.

The polysaccharide grafted MPDMA/sulfonate copolymers were testedaccording to the method employed in Example I.

                  TABLE VII                                                       ______________________________________                                        Comparative Data with Graft Copolymer                                                                    Yield                                                                         Weight                                             MPDMA/                     Per-                                               AMPS ® AMPS ®                                                                             AN     cent  XOH   DIW  SU                                Exp. Mole Percent                                                             ______________________________________                                         3B  --        --       100  50    Yes   783  36                              391  --        10       90   70    Yes   650  49                              335  19        --       79   88    Yes   478  67                              ______________________________________                                         MPDMA/AMPS ® = 3-methacrylamidopropyldimethylammonium cation              2acrylamido-2-methylpropane sulfonate anion                                   AMPS ® = 2-acrylamido-2-methylpropane sulfonate (Note: AMPS is a          trademark of Lubrizol for 2acrylamido-2-methylpropane sulfonic acid.)         AN = Acrylonitrile                                                            XOH = Basic Hydrolysis and/or Neutralization with aqueous NaOH or KOH         DIW = Deionized Water                                                         SU = Synthetic Urine                                                          Dsp = Dispersed                                                          

                  TABLE VIII                                                      ______________________________________                                        Comparative Data with Graft Copolymer                                                                   Yield                                               MPDMA/                    Weight                                              MES         MES    AN     Percent                                                                              XOH   DIW  SU                                Exp   Mole Percent                                                            ______________________________________                                        400   --        10     90   --     Yes   798  50                              366    7        --     93   67     Yes   556  80                              367   13        --     87   53     Yes   550  78                              ______________________________________                                         MPDMA/MES = 3methacrylamidopropyldimethylammonium cation                      2methacryloyloxyethane sulfonate anion                                        MES = 2methacryloyloxyethane sulfonate anion                                  AN = Acrylonitrile                                                            XOH = Basic Hydrolysis and/or Neutralization with aqueous NaOH or KOH         DIW = Deionized Water                                                         SU = Synthetic Urine                                                     

The data in Tables VII and VIII demonstrates that these polysaccharidegrafted MPDMA/sulfonate copolymers exhibit significantly improvedabsorbency to aqueous electrolyte solutions such as urine over theabsorbency of the known crosslinked polymers listed in Table III, thecommercially available materials listed in Table IV, the MPDMA/sulfonatecrosslinked homopolymers listed in Table V, and theMPTMA/AMPS-acrylamide copolymers listed in Table VII.

The absorbency of these polymers to urine is highly unexpected in viewof the fact that the homopolymers of MPDMA/sulfonate with 0.05 weightpercent cross-linking agent only absorb about 23 grams of syntheticurine per gram of the polymer. See Table V. This demonstrates that themonomers when combined into the polysaccharide grafted MPDMA/sulfonatecopolymers of the present invention act synergistically to increase theabsorbency of the polymers to aqueous liquids such as salt water andurine.

Taking an absorbency of about 37 grams of synthetic urine per gram ofpolymer as about the best of the known starch grafted polymers, thepreferred polysaccharide grafted MPDMA/sulfonate copolymers of thepresent invention exceed this absorbency to urine by 81-116 percent(67-80 grams synthetic urine per gram of inventive polysaccharidegrafted MPDMA/sulfonate copolymers, Table VII and Table VIII, comparedto 37 grams urine per gram for the best of the known starch graftedpolymers Table IV, and Table VI) without sacrificing absorbency todeionized water. These improved absorbencies translate into largesavings in the quantity of grafted polymer required and large savings tothe consumer.

Taking an absorbency of about 56 grams of synthetic urine per gram ofpolymer as about the best of the commercially available crosslinkedpolymers, the preferred polysaccharide grafted polymers of the presentinvention generally exceed this absorbency to urine by 20-43 percent(67-80 grams synthetic urine per gram of inventive polysaccharidegrafted MPDMA/sulfonate copolymers, Table VII and Table VIII, comparedto 56 gram urine per gram for the best known materials, Table III, TableIV, Table V, and Table VI) without sacrificing absorbency to deionizedwater. These improved absorbencies translate into large savings in thequantity of grafted polymer required.

We claim:
 1. A graft copolymer formed by:(A) graft polymerizing onto afirst polymer of polypropylene; at least one comonomer selected from thegroup consisting of acrylamide, methacrylamide, acrylonitrile, acrylicacid, methacrylic acid, alkali salts of acrylic acid, alkali salts ofmethacrylic acid, 2-methacrylamidopropyldimethylamine,2-acrylamido-2-methylpropane sulfonic acid, alkali salts,2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyloxyethanesulfonic acid, alkali salts of 2-methacryloyloxyethane sulfonic acid,N-vinyl-2-pyrrolidone and combinations of two or more thereof; and (B)graft copolymerizing therewith an ampholytic ion pair monomer having anammonium cation and a sulfonate anion wherein(i) the ammonium cation is3-methacrylamidopropyldimethylammonium (ii) the sulfonate anion isselected from the group consisting of 2-acrylamido-2-methylpropanesulfonate, 2-methacryloyloxyethane sulfonate, vinyl sulfonate, styrenesulfonate and any combination of two or more thereof; wherein thecomonomers and ion pair monomers are provided in amounts which areeffective to produce a highly absorbent graft copolymer; and (C)partially saponifying neutralization of said graft copolymer formed instep (B).
 2. The graft copolymer of claim 1 wherein(A) the comonomer isselected from the group consisting of acrylonitrile, acrylamide andalkali salts of acrylic acid (B) the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and a sulfonate anion selectedfrom the group consisting of 2-acrylamido-2-methylpropane sulfonate and2-methacryloyloxyethane sulfonate.
 3. The graft copolymer of claim 2wherein the graft copolymer is composed of(A) from about 1 weightpercent to about 50 weight percent of polypropylene; and (B) from about50 weight percent to about 99 weight percent of the comonomer andampholytic ion pair grafted therewith being present in the followingmole percentages:(i) from about 75 mole percent to about 98 mole percentof acrylonitrile; and (ii) from about 2 mole percent to about 25 molepercent of the ampholytic ion pair, wherein the mole percent of thecomonomer and the ampholytic ion pair total 100 mole percent.
 4. Thegraft copolymer of claim 3 wherein the graft copolymer is composed of(A)from 5 weight percent to about 30 weight percent of polypropylene; and(B) from about 70 weight percent to about 95 weight percent of thecomonomer and ampholytic ion pair grafted therewith being present in thefollowing mole percentages:(i) from about 75 mole percent to about 95mole percent of acrylonitrile; and (ii) from about 5 mole percent toabout 25 mole percent of the ampholytic ion pair, wherein the molepercent of the comonomer and the ampholytic ion pair total 100 molepercent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-acrylamido-2-methylpropanesulfonate.
 5. The graft copolymer of claim 3 wherein the graft copolymeris composed of(A) from about 5 weight percent to about 30 weight percentof polypropylene; and (B) from about 70 weight percent to about 95weight percent of the comonomer and ampholytic ion pair graftedtherewith being present in the following mole percentages:(i) from about80 mole percent to about 95 mole percent of acrylonitrile; and (ii) fromabout 5 mole percent to about 20 mole percent of the ampholytic ionpair, wherein the mole percentage of the comonomer and the ampholyticion pair total 100 mole percent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-methacryloyloxyethanesulfonate.
 6. The graft copolymer of claim 2 wherein the graft copolymeris composed of(A) from about 1 weight percent to about 50 weight percentof polypropylene; and (B) from about 50 weight percent to about 99weight percent of the comonomer and ampholytic ion pair graftedtherewith being present in the following mole percentages:(i) from about80 mole percent to about 98 mole percent of acrylamide; and (ii) fromabout 2 mole percent to about 20 mole percent of the ampholytic ionpair, wherein the mole percent of the comonomer and the ampholytic ionpair total 100 mole percent.
 7. The graft copolymer of claim 6 whereinthe graft copolymer is composed of(A) from 5 weight percent to about 30weight percent of polypropylene; and (B) from about 70 weight percent toabout 95 weight percent of the comonomer and ampholytic ion pair graftedtherewith being present in the following mole percentages:(i) from about80 mole percent to about 95 mole present of acrylamide; and (ii) fromabout 5 mole percent to about 20 mole percent of the ampholytic ionpair, wherein the mole percent of the comonomer and the ampholytic ionpair total 100 mole percent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-acrylamido-2-methylpropanesulfonate.
 8. The graft copolymer of claim 6 wherein the graft copolymeris composed of(A) from about 5 weight percent to about 30 weight percentof polypropylene; and (B) from about 70 weight percent to about 95weight percent of the comonomer and ampholytic ion pair graftedtherewith being present in the following mole percentages:(i) from about80 mole percent to about 90 mole percent of acrylamide; and (ii) fromabout 10 mole percent to about 20 mole percent of the ampholytic ionpair, wherein the mole percent of the comonomer and the ampholytic ionpair total 100 mole percent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-methacryloyloxyethanesulfonate.
 9. The graft copolymer of claim 2 wherein the graft copolymeris composed of(A) from about 1 weight percent to about 50 weight percentof polypropylene; and (B) from about 50 weight percent to about 99weight percent of the comonomer and ampholytic ion pair graftedtherewith being present in the following percentages:(i) from about 80mole percent to about 98 mole percent of alkali salt of acrylic acid;and (ii) from about 2 mole percent to about 20 mole percent of theampholytic ion pair, wherein the mole percent of the comonomer and theampholytic ion pair total 100 mole percent.
 10. The graft copolymer ofclaim 9 wherein the graft copolymer is composed of(A) from 5 weightpercent to about 30 weight percent of polypropylene; and (B) from about70 weight percent to about 95 weight percent of the comonomer andampholytic ion pair grafted therewith being present in the followingmole percentages:(i) from about 85 mole percent to about 97 mole percentof alkali salts of acrylic acid; and (ii) from about 3 mole percent toabout 15 mole percent of the ampholytic ion pair, wherein the molepercent of the comonomer and the ampholytic ion pair total 100 molepercent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-acrylamido-2-methylpropanesulfonate.
 11. The graft copolymer of claim 9 wherein the graftcopolymer is composed of(A) from about 5 weight percent to about 30weight percent of polypropylene; and (B) from about 70 weight percent toabout 95 weight percent of the comonomer and ampholytic ion pair graftedtherewith being present in the following percentages:(i) from about 90mole percent to about 97 mole percent of alkali salts of acrylic acid;and (ii) from about 3 mole percent to about 10 mole percent of theampholytic ion pair, wherein the mole percent of the comonomer and theampholytic ion pair total 100 mole percent and the ampholytic ion pairis 3-methacrylamidopropyldimethylammonium and 2-methacryloyloxyethanesulfonate.
 12. A method of absorbing an aqueous electrolyte solutioncomprising a graft copolymer form by:(A) graft polymerizing onto a firstpolymer of polypropylene; at least one comonomer selected from thegroups consisting of acrylamide, methacrylamide, acrylonitrile acrylicacid, methacrylic acid, alkali salts of acrylic acid, alkali salts ofmethacrylic acid, 2-methacryloyloxyethyldimethylamine,2-acrylamido-2-methylpropane sulfonic acid, alkali salts of2-acrylamido-2-methylpropane sulfonic acid, 2-methacryloyloxyethanesulfonic acid, alkali salts of 2-methacryloyloxyethane sulfonic acid,N-vinyl-2-pyrrolidone and combinations of two or more thereof; (B) graftcopolymerizing therewith an ampholytic ion pair monomer having anammonium cation and a sulfonate anion wherein(i) the ammonium cation is2-methacryloyloxyethyldimethylammonium; and (ii) the sulfonate anion isselected from the group consisting of 2-acrylamido-2-methylpropanesulfonate, 2-methacryloyloxyethane sulfonate, vinyl sulfonate, styrenesulfonate and any combination of two or more thereof; wherein thecomonomers and ion pair monomers are provided in amounts which areeffective to produce a highly absorbent graft copolymer; and (C)partially saponifying neutralization of said graft copolymer formed instep (B);with an electrolyte solution.
 13. The method of claim 12wherein(A) the comonomer is selected from the group consisting ofacrylonitrile, acrylamide and alkali salts of acrylic acid (B) theampholytic ion pair is 3-methacrylamidopropyldimethylammonium and asulfonate anion selected from the group consisting of2-acrylamido-2-methylpropane sulfonate and 2-methacryloyloxyethanesulfonate.
 14. The method of claim 13 wherein the graft copolymer iscomposed of(A) from about 1 weight percent to about 50 weight percent ofpolypropylene; and (B) from about 50 weight percent to about 99 weightpercent of the comonomer and ampholytic ion pair grafted therewith beingpresent in the following mole percentages:(i) from about 75 mole percentto about 98 mole percent of acrylonitrile; and (ii) from about 2 molepercent to about 25 mole percent of the ampholytic ion pair, wherein themole percent of the comonomer and the ampholytic ion pair total 100 molepercent.
 15. The method of claim 14 wherein the graft copolymer iscomposed of(A) from 5 weight percent to about 30 weight percent ofpolypropylene; and (B) from about 70 weight percent to about 95 weightpercent of the comonomer and ampholytic ion pair grafted therewith beingpresent in the following mole percentages:(i) from about 75 mole percentto about 95 mole percent of acrylonitrile; and (ii) from about 5 molepercent to about 25 mole percent of the ampholytic ion p air, whereinthe mole percent of the comonomer and the ampholytic ion pair total 100mole percent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-acrylamido-2-methylpropanesulfonate.
 16. The method of claim 14 wherein the graft copolymer iscomposed of(A) from about 5 weight percent to about 30 weight percent ofpolypropylene; and (B) from about 70 weight percent to about 95 weightpercent of the comonomer and ampholytic ion pair grafted therewith beingpresent in the following mole percentages:(i) from about 80 mole percentto about 95 mole percent of acrylonitrile; and (ii) from about 5 molepercent to about 20 mole percent of the ampholytic ion pair, wherein themole percentage of the comonomer and the ampholytic ion pair total 100mole percent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-methacryloyloxyethanesulfonate.
 17. The method of claim 13 wherein the graft copolymer iscomposed of(A) from about 1 weight percent to about 50 weight percent ofpolypropylene; and (B) from about 50 weight percent to about 99 weightpercent of the comonomer and ampholytic ion pair grafted therewith beingpresent in the following mole percentages:(i) from about 80 mole percentto about 98 mole percent of acrylamide; and (ii) from about 2 molepercent to about 20 mole percent of the ampholytic ion pair, wherein themole percent of the comonomer and the ampholytic ion pair total 100 molepercent.
 18. The method of claim 17 wherein the graft copolymer iscomposed of(A) from 5 weight percent to about 30 weight percent ofpolypropylene; and (B) from about 70 weight percent to about 95 weightpercent of the comonomer and ampholytic ion pair grafted therewith beingpresent in the following mole percentages:(i) from about 80 mole percentto about 95 mole percent of acrylamide; and (ii) from about 5 molepercent to about 20 mole percent of the ampholytic ion pair, wherein themole percent of the comonomer and the ampholytic ion pair total 100 molepercent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-acrylamido-2-methylpropanesulfonate.
 19. The method of claim 17 wherein the graft copolymer iscomposed of(A) from about 5 weight percent to about 30 weight percent ofpolypropylene; and (B) from about 70 weight percent to about 95 weightpercent of the comonomer and ampholytic ion pair grafted therewith beingpresent in the following mole percentages:(i) from about 80 mole percentto about 90 mole percent of acrylamide; and (ii) from about 10 molepercent to about 20 mole percent of the ampholytic ion pair, wherein themole percent of the comonomer and the ampholytic ion pair total 100 molepercent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-methacryloyloxyethanesulfonate.
 20. The method of claim 13 wherein the graft copolymer iscomposed of(A) from about 1 weight percent to about 50 weight percent ofpolypropylene; and (B) from about 50 weight percent to about 99 weightpercent of the comonomer and ampholytic ion pair graft therewith beingpresent in the following mole percentages:(i) from about 80 mole percentto about 98 mole percent of alkali salt of acrylic acid; and (ii) fromabout 2 mole percent to about 20 mole percent of the ampholytic ionpair, wherein the mole percent of the comonomer and the ampholytic ionpair total 100 mole percent.
 21. The method of claim 20 wherein thegraft copolymer is composed of(A) from 5 weight percent to about 30weight percent of polypropylene; and (B) from about 70 weight percent toabout 95 weight percent of the comonomer and ampholytic ion pair graftedtherewith being present in the following mole percentages:(i) form about85 mole percent to about 97 mole percent of alkali salts of acrylicacid; and (ii) from about 3 mole percent to about 15 mole percent of theampholytic ion pair, wherein the mole percent of the comonomer and theampholytic ion pair total 100 mole percent and the ampholytic ion pairis 3-methacrylamidopropyldimethylammonium and2-acrylamido-2-methylpropane sulfonate.
 22. The method of claim 20wherein the graft copolymer is composed of(A) from about 5 weightpercent to about 30 weight percent of polypropylene; and (B) from about70 weight percent to about 95 weight percent of the comonomer andampholytic ion pair grafted therewith being present in the followingmole percentages:(i) from about 90 mole percent to about 97 mole percentof alkali salts of acrylic acid; and (ii) from about 3 mole percent toabout 10 mole percent of the ampholytic ion pair, wherein the molepercent of the comonomer and the ampholytic ion pair total 100 molepercent and the ampholytic ion pair is3-methacrylamidopropyldimethylammonium and 2-methacryloyloxyethanesulfonate.